Fluid-filled type vibration damping devices suitable for example in engine mount applications to provide vibration damped support of the power unit on the vehicle body of an automobile have been proposed in the past. Such fluid-filled type vibration damping devices have a construction in which a first mounting fitting mounted onto a primary vibration system and a second mounting fitting mounted onto the vehicle body are linked to one another by a main rubber elastic body. One known type of such vibration damping device has a pressure-receiving chamber whose wall is partially defined by the main rubber elastic body and that is adapted to give rise to internal pressure fluctuations at times of vibration input, and an equilibrium chamber whose wall is partially defined by a diaphragm and that permits change in volume through deformation of the diaphragm; in this fluid-filled type vibration damping device, the pressure-receiving chamber and the equilibrium chamber are filled with a non-compressible fluid, and an orifice passage is formed connecting the pressure-receiving chamber and the equilibrium chamber with one another. At times of vibration input, this fluid-filled type vibration damping device exhibits vibration damping action based on resonance action etc. of fluid flowing through the orifice passage between the pressure-receiving chamber and the equilibrium chamber. Once such device is disclosed in Patent Citation 1.
However, a problem with fluid-filled type vibration damping devices is that while they have excellent vibration damping action based on fluid flow action against vibration of the frequency to which the orifice passage has been pre-tuned, it is difficult to attain effective vibration damping action of vibration lying outside the tuning frequency. Particularly at times of input of vibration having higher frequency than the tuning frequency of the orifice passage, because the orifice passage becomes clogged and substantially blocked off due to antiresonance, the problem of markedly diminished vibration damping capability due to a higher dynamic spring rate of the mount as a whole tends to occur.
As taught in Patent Citation 1, it has been attempted provide both a low-frequency orifice passage tuned for example to the low-frequency range of engine shake, as well as a high-frequency orifice passage tuned for example to the high frequency range of idling vibration, in order to achieve a vibration damping device capable of producing effective vibration damping action of any of multiple types of vibration of different frequency.
In such a vibration damping device furnished with multiple orifice passages, in order for the low-frequency orifice passage to have efficient high-attenuating action, the high-frequency orifice passage is designed to become blocked at times of input of vibration in the low-frequency range to which the low-frequency orifice passage has been tuned. Specifically, as taught in Patent Citation 1, on the channel of the high-frequency orifice passage there is disposed a moveable plate which is allowed to undergo displacement in the plate thickness direction, as well as a support member adapted to limit the level of displacement of the moveable plate in the plate thickness direction; and at times of input of low-frequency, large-amplitude vibration, the moveable plate is constrained by the support member so that the high-frequency orifice passage is blocked. Meanwhile, at times of input of high-frequency, small-amplitude vibration to which the high-frequency orifice passage has been tuned, fluid flow is effectively produced through the high-frequency orifice passage by minute displacements of the moveable plate.
However, even the fluid-filled type vibration damping device disclosed in Patent Citation 1 has an unresolved issue. Specifically, in the fluid-filled type vibration damping device according to Patent Citation 1, the pressure-receiving chamber and the equilibrium chamber are formed in series in the direction of the center axis to the inside peripheral side of the second mounting fitting which has circular cylinder shape; and a partition member is disposed between the pressure-receiving chamber and the equilibrium chamber, and is supported by the second mounting fitting. An orifice passage is formed in this partition member, and the moveable plate which has been arranged on the fluid channel of the high-frequency orifice passage is supported by the partition member. For this reason, the fluid-filled type vibration damping device tends to have a larger dimension in the axial direction, thus requiring a larger installation space and hampering attempts to reduce vehicle size.
Moreover, for reasons such as avoiding reduced durability of the diaphragm due to heat emitted from the engine, or avoiding pressure fluctuations arising from temperature changes in the air chamber formed between the bracket and the diaphragm, the second mounting fitting which supports the partition member is designed to be mounted on the vehicle body. Thus, when the moveable plate strikes against the partition member due to input of low-frequency, large-amplitude vibration, noise and vibration produced by this striking will be transmitted without attenuation from the second mounting fitting to the vehicle body. As a result, passengers inside the cabin may feel noise and vibration.
Prior Art Document
Patent Citation
Patent Citation 1: JP-A 1-193425